Plant prepares for pathogens at dawn

When flu season arrives, you might start eyeing citrus fruit closely or washing your hands with extra diligence. You're not alone. One species of plant, Arabidopsis thaliana, also anticipates an impending infection and guards itself against it.

The secret to its success is an immune system that is partially regulated by light, allowing it to fight off a pathogen that attacks at dawn.

Xinnian Dong of Duke University in Durham, North Carolina, and colleagues studied how a small flowering plant, Arabidopsis thaliana, defends itself against a fungus-like pathogen, Hyaloperonospora arabidopsidis, which covers the plant's leaves in a white downy mildew.

The team found that plants engineered to lack 22 genes, all partly regulated by light-driven circadian rhythms, were unable to resist attack. Plants with the genes did not succumb to the pathogen.

Dawn attack

The pathogen attacks at dawn, so to fight it the plants should raise their defences overnight. Sure enough, the team found that the 22 defence genes are all expressed in the evening

"We discovered that these defence genes have a rhythm," Dong says. "We never really thought about plants' immune systems this way, but it actually makes a lot of sense."

C. Robertson McClung, an expert on plant circadian rhythms at Dartmouth College in Hanover, New Hampshire, is excited by the study as it is the first to find a convincing mechanism for the relationship between the immune system and light.

"This is such a nice solid study that really makes it clear there is a link between timing and resistance to at least this one pathogen," McClung says. "It is really exciting and gratifying."

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